Custom Sorting

[Mike King]

Is there a way to sort by element names in XSLT, but not in ascending or
descenting order but by elements that I specify?

<root>
<cat />
<dog />
<rabbit />
</root>

the sorted result tree

<root>
<rabbit />
<cat />
<dog />
</root>

 

[Robin Johnson]

Is there a way to sort by element names in XSLT, but not in ascending or
descenting order but by elements that I specify?

<root>
<cat />
<dog />
<rabbit />
</root>

the sorted result tree

<root>
<rabbit />
<cat />
<dog />
</root>

If I understand what you're trying to do, I believe you can do it in
XSLT 1.0 if your processor supports exsl:node-set() or a similar
extension (see www.exslt.org):

<xsl:variable name="my-sort-order">
<rabbit/>
<cat/>
<dog/>
</xsl:variable>

<xsl:template match="root">
<xsl:for-each select="*">

<xsl:sort select="count(exsl:node-set($my-sort-order)/*[name() =
name(current())]/preceding-sibling::*)" data-type="number"
order="ascending"/>

<xsl:copy-of select="."/>

</xsl:for-each>
</xsl:template>

 

[Mike King]

If I understand what you're trying to do, I believe you can do it in

XSLT 1.0 if your processor supports exsl:node-set() or a similar
extension (see www.exslt.org):

<xsl:variable name="my-sort-order">
<rabbit/>
<cat/>
<dog/>
</xsl:variable>

<xsl:template match="root">
<xsl:for-each select="*">

<xsl:sort select="count(exsl:node-set($my-sort-order)/*[name() =
name(current())]/preceding-sibling::*)" data-type="number"
order="ascending"/>

<xsl:copy-of select="."/>

</xsl:for-each>
</xsl:template>

It worked! Thanks for your help.

How did you come up with this solution? I'm having a difficult time with
XSLT and I'm wondering how did you come up with this interesting solution.
Does one need to read the XSLT spec or is there a real good book that
explains XSLT. I consider myself a very technical person (I know several
programming languages) but XSLT just kicks my butt. If no one answered my
question, I was going to re-write my XSLT in C# or C++ to get the job the
done. Thanks again for your help.

 

[Robin Johnson]

[programmer-defined sort order in XSLT 1.0 using exsl:node-set()]

It worked! Thanks for your help.

Glad to hear it.

How did you come up with this solution? I'm having a difficult time with
XSLT and I'm wondering how did you come up with this interesting solution.

A diseased mind and a lot of drugs.

Tip 1: use exsl:node-set(). It makes XSLT *much* more powerful. In particular,
it's the only way you can 'sweep' twice over the same bit of source XML, i.e.
apply one template to a piece of the source, then apply a second template to
the result of that first template (the tree-shaped result, not just its
string-value.) The decision in the XSLT 1.0 spec not to allow XPath operations
on a tree-fragment variable "to allow for this to be implemented in future
versions" strikes me as truly bizarre. Thankfully XSLT 2.0 will do away with
that. (XSLT 2.0 also has a programmer-defineable sort order construct, I
believe. Michael Kay's Saxon at www.saxonica.com implements the current
working draft of 2.0, but I'm shy of working drafts so I'm sticking with 1.0
for the time being and using exsl:node-set a lot.)

Tip 2: don't be afraid to do clever things that look inefficient. If your data
is XML rather than strings, XSLT is *fast*. The only real exception I have
found to this is that in both the implementations I have used (MSXML and
Saxon), sweeping down the following-sibling:: axis is much faster than using
preceding-sibling:: (e.g. when you're trying to find the first unique value of
something - finding the last will be faster.)

Does one need to read the XSLT spec or is there a real good book that
explains XSLT.

The lovely Michael Kay strikes again: "XSLT Programmer's Reference", in the
"Programmer to Programmer" series by Wrox Press. The documentation on his site
is also very helpful.

I consider myself a very technical person (I know several
programming languages) but XSLT just kicks my butt.

"Assignment statement considered harmful."

--
Robin Johnson
rj at robinjohnson dot f9 dot co dot uk
http://www.robinjohnson.f9.co.uk

Only joking about the drugs.

 

[Ed Beroset]

A diseased mind and a lot of drugs.

Fortunately, there's not (yet) a software patent on that technique.

The lovely Michael Kay strikes again: "XSLT Programmer's Reference", in the
"Programmer to Programmer" series by Wrox Press. The documentation on his site
is also very helpful.

At the risk of posting a worthless "me too" post, I would absolutely
second this. IMHO, it is one of the very few XSLT books worth the
price. (I haven't yet found another, but my statement allows that one
might exist.)

"Assignment statement considered harmful."

Kay's corollary: "for-each usually a mistake"

Ed